Operation of thrust motors with high impulse and fuel for same



Oct. 29, 1957 F. ZWlCKY ETAL Y 2,811,431

OPERATION OF THRUST MOTORS WITH HIGH IMPULSE, AND FUEL FOR SAME Filed July 26, 1944 a T may Beast/RE FUEL 7:4 Mk V ox/a/zaq TANK ACETYLENE 0 AMMONIA I ATH/GH RfssI/R I an ELECTED MAGNET/C VAL V5 Fkl TZ Z WIC I K K ATTORNEYS Unite i.

OPERATION OF THRUST MOTORS WITH HIGH IMPULSE AND FUEL FOR SAME Fritz Zwicky, Pasadena, James M. Carter, Highway Highlands, and Frederick J. Ewing, Altadena, Calif., assignors, by mesne assignments, to Aerojet-General Cor poration, Azusa, Califi, a corporation of Ohio Application July 26, 1944, Serial No. 546,686 8 Claims. (Cl. 52.5)

1b. sec.

Many fuels capable of producing such impulses have been impractical due to the fact that their combustion temperatures and pressures have not been within reasonably workable limits. In accordance with our invention we provide a propellant fuel which develops the desired high specific impulse at temperatures and pressures well below 2600 K. and 300 lbs. per square inch respectively. An attendant advantage of our invention is the elimination of the dissociation of the combustion gases and other unfavorable gas characteristics which would be encountered at temperatures above 4000 K.

One of the most effective means of reducing the combustion temperature is the introduction of H2 gas into the combustion chamber. Practically it is difficult to supply sufiicient gaseous Hz, and the use of liquid H2 is not expedient due to its low liquid density and temperature.

According to our invention endothermic high energy fuels having at least 5% hydrogen by weight are dissolved in compounds containing nitrogen and hydrogen which decompose readily to release hydrogen. The preferred endothermic compound is acetylene and the preferred nitrogen hydrogen compound is liquid ammonia. Ammonia decomposes easily (requiring 16 K. cal/mole) at about 800 C. or less. The low temperature of combustion of this mixture prevents dissociation of the gases thereby increasing the available energy supplied to the jet motors.

Endothermic compounds other than acetylene itself which might be used are the higher members of the acetylene series, these all being referred to herein as acetylenes. Thus, for the purpose of our invention, polyacetylenes, methyl acetylene, and ethyl acetylene may be used in place of acetylene itself. Endothermic olefinic hydrocarbons having two or more double or triple bonds or a combination of double and triple bonds in the molecule such as butadiene, diacetylene, or vinyl acetylene may be substituted for acetylene. Likewise, C, H, N, compounds having at least 6% hydrogen by weight and amines with at least one amine group for every two carbon atoms, hydrazine, or mixtures of any of these with ammonia can be substituted for ammonia.

The carburetant may be oxygen, a halogen or mix- States Patent 0 ice tures of these elements, or an oxygen bearing halogen compound volatile at room temperature. Such carburetants must be used rather than atmospheric oxygen as the oxygen content of the atmosphere is too low to produce the required specific impulse. The reaction requires that an oxidizing atmosphere containing at least 60% by volume of oxygen be used before impulses above 235 lbs. sec.

Oz. The reaction which occurs is substantially as follows:

0,112 2NH3 200 E20 3H, N2

The available specific impulse from such a mixture decomposing in the manner indicated by Equation 1 is 260 lbs. sec.

at a combustion pressure of 300 lbs. per square inch and is obtained at a combustion temperature of only 2600 K. This compares favorably with ordinary hydrocarbon type of fuels such as gasoline because the maximum specific impulses available from the gasoline type of hydrocarbon fuel when burned with oxygen is less than 225 lbs. sec.

at a combustion pressure of 300 lbs. per square inch, even when the combustion temperature approaches 3000 K. and usually the order of magnitude is only between and 200 lbs. sec.

Another advantage of our invention will become apparent when considering the combustion of acetylene and oxygen alone. In absence of dissociation this would proceed according to Equation 2.

and would theoretically give combustion temperatures above 5300 C. Due to dissociation of products of combustion and other unfavorable gas characteristics, however, the actual temperature obtained is much less than 5300 C. being only in a little excess of 3000 C.

Dissociation of the products of combustion is unfavorable except in some very special cases because the energy of dissociation is of the order of magnitude of the energy of combustion. The energy absorbed by the dissociation must be recovered during the expansion process, or it will be lost. Since the time available for recombination is extremely short, being in the order of a microsecond, very little of this absorbed energy is actually recovered.

Our invention eliminates dissociation of the products of combustion and thereby achieves higher efficiency in producing a given exhaust velocity, by expanding gases from a fixed temperature and pressure, than can in general be obtained when dissociation occurs.

An advantage of our invention is demonstrated by the 3 7 addition of NHstO acetylene. The NH3 lowers the theoretical temperature of combustion when oxygen is used in proportions indicated by Equation 1 from 5300 C. to about 2300 C. Because dissociation of the gases of combustion becomes'negligible below 2400 C. there is no corresponding loss of available energy of the propellant. This is indicated by the fact that the actual tem-' perature of combustion is of the same degree of magnitude as the calculated value.

An added feature of our invention is that endothermic compounds such as acetylene can be liquefied and kept under pressure when in solution with NHa and do not undergo spontaneous decomposition as is the case when relatively pure compounds of the class of acetylene are subjected to pressure.

The drawing shows a schematic assembly partly in cross section of a system comprising a motor with fuel, oxygen and inert gas-containers, arranged to operate in accordance with this invention.

Fuel in container 1 isplaced under pressure by the inert gas in container 3 or other suitable pressurizing means,- such as a fuel pump. Constant pressure is maintained by-the pressure regulator 15 placed in the line connecting tanks-3 and 1. Oxidizer under pressure is stored in oxidizer container 2. This tank supplies oxidizer through conduit 4 and constant pressure is maintained at the valve by pressure regulator 5. Electromagnetic valves 7 and 3 permit theoperator to control the flow of fuel and oxidizer into conduits 9 and 10 which connect to jets Hand 12. A spark plug 14 or other suitable ignition means ignites the-explosive mixture near the point of intersection of the oxidizer and fuelin combustion chamber 13 of the motor.

We claim:

1. A propellant charge consisting of a mixture of a non-aromatic, fluid, endothermic, unsaturated hydrocarbon containing at least hydrogen by weight; a compound selected from the group consisting of nitrogen and hydrogen compounds containing at least one NHz group, and organic compounds of hydrogen and nitrogen, containing no additional element .other than carbon, said carbon-containing hydrogen and nitrogen compounds having at least one NHz group for every two carbon atoms; and a volatile oxidizing agent selected from the group consisting of oxygen, a halogen, mixture of halogens, and

oxygen-bearing halogen compounds, volatile at room temperature.

2. A propellant charge according to claim 1 in which the endothermic compound is a compound of the acetylene series.

3. A propellant charge consisting of a mixture in the proportions of one mole of a non-aromatic fluid, endothermic, unsaturated hydrocarbon having at leasttwo double bonds in the molecule, two moles of ammonia and one and one-half moles of a volatile oxidizing agent.

4. A propellant charge consisting of a mixture in the proportions of one mole .of a compound of the acetylene series, two moles of ammonia and one and one-half moles of a volatile oxidizing agent.

5. A propellant charge consisting of a mixture'in the proportions of one mole of acetylene, two moles of an aliphatic amine, said amine having at least one amino group to every two carbon atoms and one and one-half moles of a volatile oxidizing agent.

6. A propellant charge consisting of a mixture in the proportion of one mole of acetylene, two moles of ammonia and one and one-half moles of an oxidizing agent.

7. A propellant'charge consisting of a mixture in the proportion of one mole of butadiene, two moles of ammonia, and one and one-half moles of oxygen.

8. A propellant charge consisting of a mixture in the proportion of one mole acetylene, two moles of ammonia, and one and one-half moles of a volatile halogen.

References Cited in the file of this patent UNITED STATES PATENTS 1,408,056 Wohl Feb. 28, 1922 1,488,009 Kirby Mar. 25, 1924 1,551,650 Eglofi Sept. 1, 1925 1,856,552 Hadamik et a1 May 3, 1932 2,183,313- Goddard Dec. 12, 1939 2,217,649 Goddard Oct. 8, 1940 2,357,184- Frejacques Aug. 29, 1944 2,474,183 King June 21, 1949 FOREIGN PATENTS 15,852 Great Britain Mar. 15, 1906 of 1905 

1. A PROPELLANT CHARGE CONSISTING OF A MIXTURE OF A NON-AROMATIC, FLUID, ENDOTHERMIC, UNSATURATED HYDROCARBON CONTAINING AT LEAST 5% HYDROGEN BY WEIGHT; A COMPOUND SELECTED FROM THE GROUP CONSISTING OF NITROGEN AND HYDROGEN COMPOUNDS CONTAINING AT LEAST NH2 GROUP, AND ORGANIC COMPOUNDS OF HYDROGEN AND NITROGEN, CONTAINING NO ADDITIONAL ELEMENT OTHER THAN CARBON, SAID CAR BON-CONTAINING HYDROGEN AND NITROGEN COMPOUNDS HAVING AT LEAST ONE NH2 GROUP FOR EVERY TWO CARBON ATOMS; AND A VOLATILE OXIDIZING AGENT SELECTED FROM THE GOUP CONSISTING OF OXYGEN, A HALOGEN, MIXTURE OF HALOGENS, AND OXYGEN-BEARING HALOGEN COMPOUNDS, VALATILE AT ROOM TEMPERATURE. 